As of Tuesday evening, a virulent and mysterious type of E. coli had killed 16 people in northern Germany and Sweden and sickened 1,150 others in Germany alone.

The source of the food-borne outbreak is still unknown, though German officials had earlier suggested that the bacteria was spread on tainted cucumbers shipped from Spain. Tests of Spanish produce have not turned up the outbreak-causing E. coli strain, but German officials are still warning against eating raw cucumbers, lettuce and tomatoes.

While many food-borne E. coli infections typically cause a bad case of diarrhea (but can be fatal), the rarer serotype of E. coli circulating in Europe has caused hemolytic uremic syndrome (HUS), a potentially deadly disease that can lead to kidney failure, in at least 373 people in Germany. As public-health officials continue to try to pinpoint the source of the outbreak, food scientists and microbiologists are busy studying the genetic makeup of this particular serotype of E. coli, which may be a strain of E. coli O104:H21, according to the Washington Post.

Healthland talked with Martin Wiedmann, a professor of food science at Cornell University.

Many consumers may not know there are so many types of disease-causing E. coli.

Obviously there are vast differences between E. coli — some that cause no diseases and then types that cause severe infections. Some serotypes cause urinary tract infection, some cause diarrhea, but most don’t cause the severe type of thing we’re seeing right now. The outbreak in Germany is caused by one of the serotypes that is very severe.

There are six serotypes known as the ‘Big 6’ that are commonly associated with severe types of diseases like kidney failure, severe diarrhea. [The serotype in Germany] is a new one and it’s intriguing: one key gene we thought was important for E. coli to cause severe illness was one that encodes intimin, which allows E. coli to intimately attach to human intestinal cells. This serotype doesn’t have that gene, which is really surprising. So there’s something unusual going on; a lot of the evidence suggests it’s a very unusual bacterium.

If this type of E. coli doesn’t have the key genetic capability, how is it making people sick?

One of the other genes that’s important is carried by a virus, which can move genetic material from one bacteria to another. Phages, viruses that can infect bacteria, often introduce new genetic material, so you might see an emergence of some traits that way. They can move genetic material from one bacteria to another — including going between serotypes. One of the genes that’s important [that causes illness] is a gene that can carry toxins from one E. coli to another E. coli.

But even though some E. coli have intimin and some don’t, what seems to be the key factor is the combination of having intimin and making shiga toxins. The toxin gets into the bloodstream, causing illnesses like severe diarrhea and even kidney failure.

What’s the treatment for people with this toxin?

It’s difficult to treat. Traditionally, you’d treat it with antibiotics, which kill bacteria. But in this instance, the E. coli makes a toxin which is found in the cell, so what happens if you kill the cell? The toxin is released into the blood stream and what happens then? The infected person gets even sicker. So really you shouldn’t treat these people with antibiotics. They are trying a new therapy right now in Germany that neutralizes the toxin.

Is E. coli most often found on vegetables?

No, E. coli isn’t found there more often. It’s simply that the problem with fresh produce is you don’t cook it. Cucumbers you won’t cook. That’s what makes the presence of these organisms on fruits and vegetables more challenging. Those types of foods cause illness more often, but I wouldn’t say E. coli is found there more often.

Where does it come from?

Almost all E. coli are associated with the gastrointestinal tract of mammals — but not all, and it gets more complex. For example, E. coli O157:H7, which is similar to the serotype that caused the outbreak in this case, seems to be largely associated with cattle, and some sheep, goats and deer. It’s associated with ruminants, animals that have four stomachs that helps them to digest grass and plant material.

Human infections are often traced back to ruminant-associated sources — undercooked ground beef — but also things like apple cider that have nothing to do with cows. In these cases, maybe the apples were contaminated with deer fecal matter. Of course it’s a circular argument: because we all believe that O157:H7 will always come from ruminant digestive tracts, whenever there’s an outbreak we’re all looking for evidence of that. And if you look hard enough for something, you’re going to find it. But we’re not always 100% sure.

If the European outbreak didn’t originate in cucumbers from Spain, as German officials thought, what else could be the source of contamination?

It could have been in a production facility where the [cucumbers] were washed or sorted, if the equipment also processed something else that contained E. coli. But it could have been any number of things like wildlife fecal material in the field. Or it could have been transmitted through water; for example, if you use surface water from your fields [to water crops], it could be contaminated from birds or other wildlife.

But it could also be through humans. Someone handles produce and doesn’t follow proper procedure for hand washing.

Aside from obvious things like hand washing, what are the best ways to avoid food-borne illness?

The problem with all this is that it really is everyone’s responsibility and everyone contributes their part to it. Beyond the specific outbreak, [it’s important to] have practices on fields to minimize the presence of animals and to have proper procedure in processing, including testing the environment to see whether E. coli is present.

Also, basic things that you’ve always been taught: don’t use the same cutting board for chicken and salad. Wash your produce. Cook things through. A major source of E. coli poisoning is still undercooked ground beef. Don’t make it medium rare or rare. There needs to be a responsibility to everyone along the whole chain.

In each case you need to identify the batch, lot, production site and then responsibly remove it. Find out its source, because you need to stop people from handling other produce that might be contaminating other products. If the field is the source and you regrow something on the same field the next year, you could have contamination then as well.

The other thing with E. coli is it can be transmitted from person to person — 20% or 30% of an outbreak is from person to person. A kid gets it, has diarrhea at nursery school and now his teachers and classmates have been exposed. So a large percentage is secondary cases as opposed to primary cases, which come from people who ate the cucumbers or whatever it is themselves. They are sick, but they cook food, handle people in a public setting and then they can contribute to contamination.

And I should say that we are getting better at identifying disease than we have ever been. We have better public health systems now than we did even 15 or 20 years ago. That’s because we have fingerprinting tools that we can use. We are at the point where if one person gets sick with E. coli in California, another in Kansas, another in Michigan and samples are sent to the CDC, they can now actually trace it back to the food source and identify groups of people who got sick from the one batch.